Thermoplastic polyester resins such as poly(ethylene terephthalate) are used for various industrial purposes in the form of fiber or film since they are excellent in heat resistance, chemical resistance, weatherability, mechanical properties, electric properties, molding flowability and the like. However, higher mechanical properties and heat resistance are further required. Attempts have been made to mix various fillers, examples of which are inorganic fiber such as glass fiber, carbon fiber and potassium titanate whisker, and inorganic particles such as glass flakes, glass beads, talc, mica and kaolin. Though mechanical properties and the like are actually improved by mixing the above inorganic materials, there is a problem that appearance is lost due to the emergence of fibrous reinforcements and specific gravity is increased. There is also a problem that anisotropy occurs due to orientation of inorganic fibers.
It is generally thought that these defects in mixing inorganic fiber and inorganic particles are caused by the fact that dispersion of inorganic materials is insufficient and dispersion particle size thereof is too large.
As an attempt to disperse layered phyllosilicate among inorganic materials into a thermoplastic resin, there is disclosed (1) invention relating to a resin composition containing a layered inorganic filler and a thermoplastic polyester resin, wherein the layered inorganic filler has 0.2 to 1.0 of a charge on the layers and basal space expanded at least five times the initial value (Japanese Unexamined Patent Publication No. 26123/1995). Specifically, the disclosed technology is such that swellable mica is used as layered phyllosilicate and that a polyester resin composition is obtained by polymerization after ester exchange reaction of ethylene glycol and dimethyl terephthalate in which the above mica is dispersed. However, a polyester resin composition having desired properties cannot be prepared according to the above invention.
In addition, there are disclosed (2) invention relating to a resin composition obtained by dispersing layered phyllosilicate in a crystalline thermoplastic resin as a crystalline nucleus at molecular level under aspect ratio of at least 20 (Japanese Unexamined Patent Publication No. 183910/1997); and (3) invention relating to a resin composition obtained by dispersing, in a thermoplastic resin, layered phyllosilicate having average layer thickness of 25 to 1,000 Å and aspect ratio of 20 to 200 (Japanese Unexamined Patent Publication No. 124836/1997). Specifically, the disclosed technology is such that swellable mica is used as layered phyllosilicate and that a resin composition is obtained by extruding swellable mica swelled in water or alkyl ammonium-treated swellable mica swelled in xylene with polypropylene or the like by using a twin-screw extruder. However, it was impossible to prepare a polyester resin composition having desired properties even by the above inventions.
The reason why a polyester resin composition having desired properties cannot be prepared by the above prior arts (1), (2) and (3) is insufficient dispersion of layered phyllosilicate. Though the basal space of swellable mica is actually expanded from the initial value, the layered phyllosilicate is not finely dispersed into the thermoplastic polyester resin but only in the state of coagulation according to the prior art (1). In addition, even if the prior arts (2) and (3) are directly applied to a thermoplastic polyester resin, dispersion of layered phyllosilicate is still incomplete and inhomogeneous though fine dispersion is partly observed.
Having excellent mechanical properties and heat resistance, reinforced polyester resins containing a thermoplastic polyester resin and a fibrous filler are used for various purposes including electronic or electric parts, exterior materials for automobiles, household electric appliances, mechanical or machinery parts and the like. However, there were problems with the above polyester resin such that dimensional accuracy of the obtained molded article significantly decreased due to orientation of the fibrous filler during injection molding. As a means for improving the above problems, processes for combining glass fiber with other inorganic fillers have been attempted. Examples thereof include (4) adding a non-fibrous inorganic substance to poly(ethylene terephthalate) and glass fiber (Japanese Unexamined Patent Publication No. 74852/1979); (5) combining fragmentized mineral fiber with poly(butylene terephthalate) and glass fiber (GF) (Japanese Unexamined Patent Publication No. 254655/1986); (6) combining mica with poly(ethylene terephthalate) and glass fiber (Japanese Unexamined Patent Publication No. 59661/1987); and the like.
However, the above prior arts (4) to (6) did not show sufficient improving effect on dimensional accuracy when the amount of the inorganic filler was small. On the contrary, when a large amount of the inorganic filler was used in order to improve dimensional accuracy, there arise different problems with increase in specific gravity, deterioration in appearance of a molded article, decrease in strength and the like.
It is thought that these defects in mixing the above inorganic filler are caused by the fact that dispersion of inorganic materials is insufficient and dispersion particle size thereof is too large. Though there are disclosed the above prior arts (1) to (3) as an attempt to finely disperse layered phyllosilicate out of organic materials into a thermoplastic resin, improvement effect on dimensional accuracy was insufficient even in the reinforced polyester resins because uniform dispersion of the layered phyllosilicate was impossible as mentioned above.
Besides, thermoplastic polyester resins have disadvantages of inferior impact resistance and dimensional stability though it shows the above characteristics. Meanwhile, aromatic polycarbonate resins are widely used, as thermoplastic resins excellent in heat resistance, impact resistance, toughness and the like, for parts of machines, automobiles, electric and electronic devices. However, relatively high processing temperature of about 300° C., high injection speed and high injection pressure are normally required for ensuring molding flowability. In addition, aromatic polycarbonate resins have problems with chemical resistance such that the surface of the molded article is cracked, deformed or dissolved due to various organic solvents or gasoline. There are also weatherability problems such as crack propagation and discoloration into yellow on the surface of the molded article in case of long exposure to ultraviolet ray.
In order to overcome these defects by making use of the respective features, resin compositions comprising a polyester resin and a polycarbonate resin are disclosed, for example, in Japanese Examined Patent Publication No. 14035/1961, Japanese Examined Patent Publication No. 20434/1964, Japanese Unexamined Patent Publication No. 176345/1984, Japanese Examined Patent Publication No. 94350/1980, Japanese Unexamined Patent Publication No. 83158/1988 and the like.
In case of forming a composition by mixing a polyester resin and a polycarbonate resin, impact resistance and dimensional stability of a polyester resin and molding flowability and chemical resistance of a polycarbonate resin are actually improved, but improvement effect on mechanical properties such as flexural modulus and heat resistance is insufficient. It is said that this is because crystallization of the polyester resin is prevented and crystallinity is lowered since the polycarbonate resin and the polyester resin are partly compatibilized or reacted with each other. Due to these phenomena, the obtained composition did not have satisfactory chemical resistance.
It has been attempted to promote crystallization of polyester resins for the purpose of improving mechanical properties and heat resistance. However, there was a problem that the polycarbonate resin is decomposed and foamed in case of using an organic carboxylate salt nuclear agent (Japanese Examined Patent Publication No. 29977/1971, Japanese Unexamined Patent Publication No. 158452/1979 and the like). Also, effects were insufficient in case of using an inorganic nuclear agent (Japanese Examined Patent Publication No. 38707/1971, Japanese Examined Patent Publication No. 27142/1972 and the like).
Though the above prior art (3) is disclosed as a different method, the layered phyllosilicate is not uniformly dispersed in the whole system but only in some part as mentioned above, making it impossible to obtain a resin composition having desired properties even if the thermoplastic resin composition contains a polycarbonate resin. In addition, when swellable mica treated with alkyl ammonium or the like is used, there arise other problems with lowering in properties and coloring due to deterioration of the polyester resin and the polycarbonate resin. Therefore, no technology is available yet at present as to obtaining a resin composition excellent in mechanical properties and heat resistance by finely dispersing layered phyllosilicate into a polyester resin and a polycarbonate resin.
An object of the present invention is to solve these conventional problems and to provide a thermoplastic resin composition and a process for preparing the thermoplastic resin composition, wherein mechanical properties, heat deformation temperature, dimensional stability and moldability are improved without losing surface properties and appearance by separating and exfoliating each unit layer of layered phyllosilicate to divide one coagulated particle of the layered phyllosilicate into numerous, extremely fine laminar particles and by dispersing the same in a thermoplastic polyester resin independently and uniformly. Another object of the present invention is to provide a reinforced thermoplastic resin composition having improved dimensional accuracy and a thermoplastic resin composition having improved mechanical properties and heat resistance without deterioration of resins, foaming, lowering of surface properties and decrease in dimensional stability.